Plasma accelerator having a cooled preionization chamber



' Feb. 20, 1968 K. c. ROGERS ET AL 3,370,198

PLASMA ACCELERATOR HAVING A COOLED PREIONIZATION CHAMBER 2 Sheets-Sheet 1 Original Filed Oct. 21, 1964 INVENTORS. KENNETH C. RQGERS 8 DONARD R. SIMON AfiW-whWA ATTORNEYS their Feb. 20, 1968 K. c. ROGERS ET AL 3,370,198

PLASMA ACCELERATOR HAVING A COOLED PREIONIZATION CHAMBER Original Filed Oct. 21, 1964 2 Sheets-Sheet 2 INVENTORS. KENNETH 0. ROGERS 8 DONARD R. SIMON their arrok/vars United States Patent 3,370,198 PLASMA ACCELERATOR HAVING A COOLED PREIONIZATION CHAMBER Kenneth C. Rogers, 50 Riverside Drive, New York, N.Y.

10024, and Donald R. Simon, 73 Fichter Sh, Bloomingdale, NJ. 07403 Continuation of application Ser. No. 405,517, Oct. 21, 1964., This application June 21, 1967, Ser. No. 647,878

16 Claims. (Cl. 315111) This application is a continuation of application, Ser. No. 405,517, filed Oct. 21, 1964 and now abandoned.

The invention relates in general to a plasma accelerator and more particularly to a plasma accelerator in which a triggering pulse across a first pair of electrodes preionizes the working substance prior to the subsequent accelerating discharge of the main electrical energy storage system. The working substance is partially ionized by surface ionization and more completely ionized by collison ionization.

Basically the plasma accelerator or gun is a coaxial electrode system relying on the (JXB) force in an axial direction to perform the desired work on the plasma. Specifically, this invention provides a method for accelerating alkaline metal plasmas and other plasmas tovelocities in the order of centimeters per second wherein the efiiciency of the energy transfer to a plasma is much higher than any other method presently known.

Heretofore, when using the old methods for performing this function such as exploding wires, gas ejection and back-strap acceleration, the major portion of ionization occurred during the main capacitor discharge. This resulted in a slow ignition current rise and large deposits of energy in the internal modes of the plasma. Furthermore, these devices were not only very inefiicient in operation but could not accelerate to high velocities a heavy working substance and use pure alkaline metals as plasmas.

This invention calls for the placing of alkaline metals or other materials which are to be accelerated in positions adjacent the terminal surfaces of two insulated electrodes which are connected through a switch-controlled circuit to a first potential storage unit. In some embodiments the plasmoid material to be accelerated is deposited in part on the cooled surface of one of these two first potential electrodes by condensation of the vaporized pla'smoid material or by other means. In all cases, however, the potential first discharges in an arc between these two electrodes and, through the material to be accelerated, vaporizing and preionizing the plasmoid material in its path. This working substance expands and closes the gap between one of these first potential electrodes and a third high potential electrode which, when the gap is sufficiently closed, discharges through the vaporized and preionized material accelerating it in the form of plasma down the coaxial accelerator tube at extremely high velocities.

This invention preionizes and rapidly ejects the working plasma, permilting the use of extremely fast capacitors and thereby permitting the use of alkaline metals as a working fluid. The preionization step, coupled with the use of fast capacitors, allows much higher efficiences and velocities to be reached than was heretofore possible when using the prior art methods.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawing, in which:

FIGURE 1 shows a cross section, elevational view of the plasma accelerator disclosed in this invention; and

FIGURE 2 shows a partially cut away isometric view of the plasma accelerator of FIG. 1.

With reference to the drawings, the invention is illusstored in chamber 18 in tank 20 prior to its delivery to the area between the first and second inner electrodes.

In the lpreferred embodiment the material to be accelerated 19 is either cesium or potassium. As shown in FIG. 1, the cesium 19 is heated in chamber 18 by electrically controlled heated elements 22 to a temperature above its melting point. Thereafter, cesium vapor passes from chamber 18, through conduit 24, control valve 26 and through conduit 28 in the large cylindrical portion 31 of first electrode 14. The conduit 28 directs the cesium vapor to cylindrical chamber 30 in the elongated tubular portion 29 of first inner electrode 14 which, in turn, leads to an area between the terminal end 76 of the first electrode 14 and the terminal end 78 of the second elec trode 16.

Within chamber 30 the tubular conduit portion 32 of second inner electrode 16 passes through the center of the first inner electrode 14 and is spaced therefrom by insulating elements 34 and 36. The tubular portion 32 of second inner electrode 16 is held firmly in place by sup porting section 37 which also houses the means for delivering and exhausting coolant 41 to and from chamber 42 within the second inner electrode 16.

The coolant 41 118 delivered through conduit 40 which passes from support 37, through hollow tube 31, into chamber 42 within inner electrode 16. The coolant, which in the preferred embodiment is liquid nitrogen, then circulates within chamber 42 and exits through the channel 38 formed between the external surface of conduit 40 and the inner surface of tubular conduit portion 32 of second inner electrode 16. The coolant 41 then passes through to the channels within supporting elements 37 electrode 14 is connected through insulating material 36 to the outer surface of tubular conduit 32. This end portion 31 is then connected through electrically conductive studs 46 and the first terminal ring 48 on high potential capacitor 50. Another portion of. cylindrical end 31 of first inner electrode 14 is then connected through fastening element 54 and electrical lines 52a and 52b to tubular portion 32 of the second inner electrode 16 by fastening means 60. Line 52a, however, first passes through the elec trical storage capacitor 56 and switch element 58, which, prior to firing of the plasma accelerator, is maintained in the open position shown schematically in. FIG. 1.

The opposite end of capacitor 50 is connected to second terminal ring 62 which, in turn, is fastened to electrical conductive tube 64 by fastening means 66. The tube 64 is held in position by insulating ring 68 which surrounds and is directly adjacent the outer surface of the tubular por= tion 29 of first inner electrode 14. Capacitor 50 is also electrically insulated by shield 49 from all of the elements adjacent to it with the exception of terminal rings 48 and 62.

In the preferred embodiment, both the first capacitor 56 and the main low-inductance, high-energy storage ca= pacitor 50 have been precharged by electrical energy sources which are not shown.

Outer electrode 12 is tubular in. shape and is held in its position concentric with the first and second inner electrodes 14 and 16, respectively, by electrical ring 64, The opposite end of outer electrode 12 engages shield 69 which forms a chamber 70. The chamber 70 is, in turn, con nected with the area 74 between the outer electrode .12 and the inner electrodes 14 and 16, the chanel area 30, the conduit areas 28 and 24, and the area within chamber 18. The space between the inner surface 13 of the electrode 12 and the outer surface of the electrode 16 forms an acceleration chamber which also directs the gas in the desired direction upon discharge of the condenser 50 between. those electrodes. All of these areas are vacuum sealed and are designed to maintain a pressure of about torr when a vacuum is provided through line 72 by a. acuum pump (not shown).

The extreme end portion 76 of first inner electrode 14 is, in the preferred embodiment, composed of tungsten as is the entire outer section 78 of second inner electrode 16, The inner surface 13 of the outer electrode 12 is, on the other hand, in the preferred embodiment, made from tantalum. The surfaces 76 and 78 are shown in the preferred embodiment in a nonparallel arrangement, the surfaces diverging slightly toward the inner surface 13 of outer electrode 12, The space between the surfaces 76 and 78 defines a preionization chamber for the material to be accelerated. The outer end portion 80 of second inner electrode 16 is composed of a conducting nonmagnetic material and serves as a guide for the accelerated plasma without adversely influencing its movement toward chamber 70.

The plasma accelerator 10 is placed in an operative condition by first energizing heating element 22 and vaporizing the cesium 19 Within chamber 18. The heated cesium vapor at approximately 100 F. passes through chamber .24 when valve 26 is open, entering conduit 28, which, in turn, in some embodiments may be separately heated by additional electrical elements. The cesium vapor passes through conduit 28 to tubular channel 30 whereupon it passes along the outer surface of insulator element 34 which surrounds tubular portion 32 of second inner electrode 16, The cesium vapor then emerges from channel 30 in the circular area adjacent the diverging surfaces 76 and 78 of the first and second inner electrodes 14 and 16, respectively.

Surface 78 in the preferred embodiment is maintained at a low temperature by the passing of liquid nitrogen 41 through conduit 40 and into inner chamber 42. At this point, a portion of the cesium vapor comes in contact with the cold tungsten surfaces 76 and 78 and solidifies, or condenses, on both of these surfaces, although the primary deposit is on surface 78. In the preferred embodiment, when the cesium vapor is in the area adjacent surfaces 76 and 78 and a certain portion of the cesium vapor has been deposited on the tungsten surfaces, the plasma accelerator 10 is ready to be discharged.

The preionization occurs when switch 58 is closed and the energy stored in. the first capacitor 56 discharges in an electric are between surfaces 76 and 78. This triggering pulse causes a substantial degree of surface ionization, thermal ionization, and electron impact ionization of the cesium. deposited on these two surfaces.

The conventional current flow for the triggering pulse passes from surface 76, through portions 29 and 31 of first inner electrode 14, through stud 46, fastening element 54, line 52a, capacitor 56, switch 58, line 52b, fastening element 60, tube portion 32 and surface 78, respectively, of second inner electrode 16', and across the gap between the surfaces 76 and 78.

The cesium electric arc discharge between surfaces 76 and 78 extends outwardly toward the inner tantalum surface 13 of outer electrode 12 and, when the gap has been sufficiently closed, the low-inductance, high-energy storagecapacitor 50 discharges circumferentially between surface 76 and the inner surface 13 at many points along both surfaces,

The conventional current flow for the main capacitor circuit: passes from surface 76, through portions 29 and 31 of first electrode 14, through studs 46, first terminal ring 48, main capacitor 50, second terminal ring 62, studs 66, conductive tube 64, outer electrode 12, a d cross 45 the gap between the inner tantalum surface 13 of the outer electrode 12 and the surface of second electrode 16 to surface 78 of electrode 16 to surface 76 of electrode 14.

In the preferred embodiment the cesium vapor in cham ber 74, and generally adjacent surfaces 76 and 78, and. the inner surface of outer electrode 12 is preionized to a large extent by three separate actions prior to the discharge of the main capacitor. First, surface ionization between the cesium and tungsten adjacent surfaces 76 and 78, secondly heating of the cesium vapor by the electric current flowing between surfaces 76 and 78 as the capacitor 56 is discharged, and thirdly, surface ionization at tantalum surface 13.

In view of the preionization of the cesium vapor between the first inner electrode 14 and the electrode 16, substantially all of the 20,000 volts of the low-inductance, high-energy storage capacitor 50 acts 'to accelerate the cesium. Thus, in the instant invention only a minimum of the energy released by the main capacitor 50 is used to ionize the vapor.

Although the invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only 'by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as herein claimed. For example, as mentioned above, the Working material may be any alkaline metal or any other element rather than cesium that can be ionized by surface ionization, e.g. barium or rhenium, as described in the preferred embodiment. Furthermore, embodiments within the scope of this invention are envisioned which do not use the vapor of the material. but rather only the solid or liquid of the material.

What is claimed is:

1. A plasma accelerator comprising a first electrode having a first surface,

a second electrode having a second surface spaced from the first electrode surface to form a preionization chamber,

means for cooling at least one of the first and second electrode surfaces,

means for introducing a vaporized material to be ac" celerated into the preionization chamber between the first and second electrode surfaces to condense and deposit the material on at least the cooled electrode surface,

a third electrode spaced from and cooperating with said first and second electrodes,

means for establishing a first electrical potential to provide a first are discharge between said first and second electrode surfaces for vaporizing and preionizing the material deposited on the cooled elec trode surface and for preionizing .the vaporized material in the preionization chamber,

the first arc discharge narrowing the electrical gap between the third electrode and at least one of the first and second electrodes and propelling the preionized material into said gap, and

means for establishing a second electrical. potential to provide a second arc discharge when the first arc discharge sufiiciently narrows the gap between the third electrode and at least one of said first and second electrodes, the second arc discharge accelerating the preionized material from said electrodes.

2. A plasma accelerator as defined in claim 1, wherein the electrode surfaces are opposed conical surfaces which diverge radially toward said third electrode,

3. A plasma accelerator as defined in claim 1, wherein the material is an alkaline metal.

4. A plasma accelerator as defined in claim 1, wherein the material is cesium.

5. A plasma accelerator as defined in claim 1, wherein the material is potassium,

6. A plasma accelerator as defined in claim 1, wherein the cooling means comprises liquid nitrogen.

7. A plasma accelerator comprising a first inner electrode having a first conical surface,

a second inner electrode concentric with the first inner electrode and having a second conical surface spaced from and opposed to the first conical surface to form a preionization chamber,

means for cooling at least one of the first and second conical surfaces,

means for introducing a vaporized alkaline metal to be accelerated into the preionization chamber between the first and second conical surfaces to deposit the alkaline metal on at least the cooled conical surface,

a third outer electrode concentric with and surrounding the first and second inner electrodes,

means for establishing a first electrical potential to provide a first arc discharge between said first and second conical surfaces for vaporizing and preionizing the alkaline metal deposited on the cooled conical surface and for preionizing the vaporized alkaline metal in the preionization chamber,

the first arc discharge narrowing the electrical gap between the third electrode and at least one of the first and second electrodes and propelling the preionized alkaline metal into said gap, and

means for establishing a second electrical potential to provide a second arc discharge when the first arc discharge sufi'iciently narrows the gap between the third electrode and at least one of said first and second electrodes, the second arc discharge accelerating the preionized alkaline metal from said electrodes.

8. A plasma accelerator as defined in claim 7, wherein the alkaline metal is cesium.

9. A plasma accelerator as defined in claim 7, wherein the alkaline metal is potassium.

10. A plasma accelerator as defined in claim 7, wherein the cooling means comprises liquid nitrogen.

11., A plasma accelerator as defined in claim 7, wherein the first and second conical surfaces diverge radially toward said third electrode.

12. Apparatus for generating a high velocity plasma compnsmg:

means for vaporizing an ionizable material;

means defining a preionization chamber for receiving the vaporized material;

means associated with the preionization chamber cooling the vaporized material to convert a major part of the introduced vaporized material into a deposit in the preionization chamber;

means for establishing a first electric arc discharge effective to revaporize and simultaneously preionize the deposited material to form a plasma;

means defining a plasma acceleration chamber com municating with the preionization chamber to re ceive the preionized material; and

means for establishing a second electric arc dis-charge in the acceleration chamber upon passage of the preionized material thereinto, thereby to propel the preionized material in a direction determined by the geometry of the acceleration chamber 13. Apparatus as defined in claim 12, in which:

the preionization chamber has an annular configura tion defined between first and second electrodes upon the surface of at least one of which the vaporized material is deposited, and

the acceleration chamber is tubular about an axis sub stantially normal to the annular ionization chamber.

14. Apparatus as set forth in claim 13, in which:

the ionization and acceleration chambers communicate over an annular area to effect radial outward mo tion of the preionized material from the preionization chamber into the acceleration chamber;

15. In combination with the apparatus defined in.

claim 12:

a potassium alkaline metal material to be vaporized by the vaporizing means,

16. In combination with the apparatus recited in claim a cesium alkaline metal material to be vaporized by the vaporizing means,

References Cited UNITED STATES PATENTS 2,883,568 4/1959 Beam 313-230 3,151,259 9/1964 Gloersen a, 328233 3,209,189 9/1965 Patrick W 31363 3,221,212 11/1965 Gorowitz 315111 45 JAMES W. LAWRENCE, Primary Examiner,

STANLEY D. SCHLOSS'ER, Examiners 

1. A PLASMA ACCELERATOR COMPRISING A FIRST ELECTRODE HAVING A FIRST SURFACE, A SECOND ELECTRODE HAVING A A SECOND SURFACE SPACED FROM THE FIRST ELECTRODE SURFACE TO FORM A PREIONIZATION CHAMBER, MEAND FOR COOLING AT LEAST ONE OF THE FIRST AND SECOND ELECTRODE SURFACES, MEANS FOR INTRODUCING A VAPORIZED MATERIAL TO BE ACCELERATED INTO THE PREIONIZATION CHAMBER BETWEEN THE FIRST AND SECOND ELECTRODE SURFACES TO CONDENSE AND DEPOSITE THE THE MATERIAL ON AT LEAST THE COOLED ELECTRODE SURFACE, A THIRD ELECTRODE SPACED FROM AND COOPERATING WITH SAID FIRST AND SECOND ELECTRODES, MEANS FOR ESTABLISHING A FIRST ELECTRICAL POTENTIAL TO PROVIDE A FIRST ARC DISCHARGE BETWEEN SAID FIRST AND SECOND ELECTRODE SURFACES FOR VAPORIZING AND PREIONIZING THE MATERIAL DEPOSITED ON THE COOLED ELECTRODE SURFACE AND FOR PREIONIZING THE VAPORIZED MATERIAL IN THE PREIONIZATION CHAMBER, THE FIRST ARC DISCHARGE NARROWING THE ELECTRICAL GAP BETWEEN THE THIRD ELECTRODE AND AT LEAST ONE OF THE FIRST AND SECOND ELECTRODES AND PROPELLING THE PREIONIZED MATERIAL INTO SAID GAP, AND MEANS FOR ESTABLISHING A SECOND ELECTRICAL POTENTIAL TO PROVIDE A SECOND ARC DISCHARGE WHEN THE FIRST ARC DISCHARGE SUFFICIENTLY NARROWS THE GAP BETWEEN THE THIRD ELECTRODE AND AT LEAST ONE OF SAID FIRST AND SECOND ELECTRODES, THE SECOND ARC DISCHARGE ACCELERATING THE PREIONIZED MATERIAL FROM SAID ELECTRODES. 